It is common practice in the manufacture of automobiles and trucks to provide, in the instrument cluster, a combined speedometer/odometer device. The reason for integrating odometers with speedometers is that they each can perform their measuring function based upon the same signal, namely, the speed of rotation of the propeller shaft or axle. The signal is capable of being translated into speed in whatever units desired, as for example, miles per hours or kilometers per hour, and also into distance traveled, the speed of rotation being translatable into miles of kilometers.
Commonly, two odometers are provided. One of the odometers gives a permanent reading of the distance the vehicle has traveled during its lifetime. This is usually measured in an amount up to 100,000 or an equivalent number of kilometers. Under existing governmental regulations, this odometer is not allowed to be reset to a zero position. A second odometer is usually provided to give distance traveled for specific purposes, such as to measure the length of a trip, to permit measuring of gas mileage and the like. It is desirable for this odometer to be resettable to a zero position so that the driver may begin any measurement desired from a zero start position. In this way, he does not have to record the initial mileage of the odometer and substract it from the total after his measurement has been taken. Normally, the total measurable distance of a resettable odometer is a great deal less than that provided for on the permanent odometer reading, as for example 1000 total miles.
It is desired that the resettable odometer be easily manipulated by the driver to the zero position. In the past, such odometers have frequently been provided with a reset knob which requires the driver to watch the setting so that he will stop the resetting procedure when the zero position has been reached. A reset mechanism which automatically sets the odometer at the zero position without the driver making observations is desired. Additionally, it is required that such a reset mechanism be quickly operable so as not to divert the attention of the driver for any considerable period of time.
One problem in providing such a reset mechanism for odometers which are commonly used in the automotive industry is that the standard resettable odometer requires turning of the odometer reset shaft an angular distance greater than 360.degree.. If the reset mechanism operates on the principal of a rotatable device, there is an inherent difficulty in causing the reset rotation movement to be set at an angular distance of greater than 360.degree. because some kind of a stop mechanism has got to be provided within the circle of rotation. Since this circle has a maximum angularity of 360.degree., any single stop mechanism provided cannot exceed this angularity. The desired angularity is provided for in the present invention by the provision of two members, the first of which does not contact the second until a certain angular distance has been traveled, thereby permitting greater than 360.degree. rotation for the reset purposes.